Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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865
FXUS66 KSEW 121106
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
306 AM PST Wed Dec 12 2018

.SYNOPSIS...After a brief lull today, expect more rain and heavy
mountain snow tonight in to Thursday. Expect windy conditions
along the coast and north interior. Another wet system will reach
the area Friday night, then a break on Saturday. Additional
fronts will affect the area early next week keeping the pattern
active.

&&

.SHORT TERM...Heavy snow showers continue this morning in the
Cascades, especially in King and Snohomish counties due to a
strong Puget Sound Convergence Zone. Models show the PSCZ
persisting into the morning hours. After a brief break this
afternoon, another round of heavy rain and mountain snow is
expected tonight as our next system moves in. We`ll see another
1-3 feet of new snow across the west slopes of the Cascades -
Winter Storm Warnings are in effect. The highest amounts will be
at the volcanoes. Snoqualmie Pass may only see 6 inches but could
see a foot at Stevens Pass. Snow levels will rise Thursday
afternoon with a warm front for mainly rain at the passes.

In addition, it`ll be windy tonight and Thursday, mainly along the
coast and in the north interior. Expect south winds of 25-35 MPH
with gusts to 50 MPH - a Wind Advisory is in effect.

The models have changed their tune on Friday. It seems our next
frontal system, at least according to the ECMWF and Canadian,
will stall offshore. So we`ll see a brief lull in this period.
Then more rain and mountain snow as we move into Friday night. The
snowpack will keep piling up with snow levels around 2000 feet.

A ridge will bring another break in the action on Saturday.
Temperatures are close to normal through the period. 33

.LONG TERM...The weather pattern will remain active through early
next week due to strong, moist SW flow over the Pac NW. This
means more rain and mountain snow through the period. The ECMWF
hints at a break late next week but for now will lean toward
persistence. 33

&&

.AVIATION...Showers continue to move onshore over Western
Washington early this morning in post-frontal westerly flow
aloft. The air mass remains fairly moist and somewhat unstable.
A convergence zone persists over eastern King County this
morning, but should gradually diminish later this morning as low
level onshore flow weakens and gradients begin to reverse in advance
of the next frontal system approaching the offshore waters.
Generally, VFR conditions are expected through the morning across
most of the region with a few showers.

High and mid level moisture will begin to thicken again by 18Z.
Rain will develop along the coast by mid afternoon as another warm
front lifts northward over the offshore waters. MVFR conditions in
rain expected along the coast by 21Z...spreading into the Puget
Sound area by mid-evening. Gusty southerly surface winds
will rise once again this evening ahead of the next front. Low level
wind shear becomes a possibility after 03Z this evening with 2000
foot winds of 40 to 45 knots possible.

KSEA...Mainly VFR expected through the morning with flow aloft
favoring some rain shadowing by the Olympics and convergence zone
activity remaining north of the terminal. MVFR conditions in rain
developing near or after 00Z and persisting well into Thursday.
Surface winds S-SW 8-14 knots though early afternoon...becoming
southerly 15 gusting 20-25 knots tonight.    27

&&

.MARINE...Cold front exiting the area. Small craft and gale
force westerlies remain in its wake early this morning. Winds will
briefly subside a bit today in between storms but that will be short-
lived. Next system approaches the coast this afternoon and moves
inland tonight into Thursday. Winds will again pick up this
afternoon/evening with another round of small craft advisories and
gale warnings. Additional systems past Thursday will impact the area
with small craft or gale conditions from time-to-time into next
week. CEO

&&

.HYDROLOGY...The Skokomish river in Mason county crested in minor
flood stage overnight. The river will slowly recede today then
rise tonight and Thursday due to another round of heavy rain in
the basin. Moderate flooding is forecast with this next wave.
Other rivers flowing of the Olympics will be monitored. Otherwise,
additional flooding is not expected. 33

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...Winter Storm Warning from 6 PM this evening to noon PST Thursday
     for Cascades of Pierce and Lewis Counties-Cascades of
     Whatcom and Skagit Counties.

     Winter Storm Warning until noon PST Thursday for Cascades of
     Snohomish and King Counties.

     Wind Advisory from 6 PM this evening to noon PST Thursday for
     Admiralty Inlet Area-San Juan County-Western Skagit County-
     Western Whatcom County.

     Wind Advisory from 6 PM this evening to 6 AM PST Thursday for
     Central Coast-North Coast.

PZ...Small Craft Advisory for rough bar until 4 PM PST Thursday for
     Grays Harbor Bar.

     Gale Warning until 7 AM PST Thursday for Coastal Waters From
     Cape Flattery To James Island 10 To 60 Nm-Coastal Waters
     From Cape Flattery To James Island Out 10 Nm-Coastal Waters
     From James Island To Point Grenville 10 To 60 Nm-Coastal
     Waters From James Island To Point Grenville Out 10 Nm-
     Coastal Waters From Point Grenville To Cape Shoalwater 10
     To 60 Nm-Coastal Waters From Point Grenville To Cape
     Shoalwater Out 10 Nm-West Entrance U.S. Waters Strait Of
     Juan De Fuca.

     Gale Warning until 7 AM PST this morning for Admiralty Inlet-
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance
     U.S. Waters Strait Of Juan De Fuca.

     Gale Warning from 4 PM this afternoon to 7 AM PST Thursday for
     Admiralty Inlet-East Entrance U.S. Waters Strait Of Juan De
     Fuca-Northern Inland Waters Including The San Juan Islands.

     Small Craft Advisory until 4 AM PST early this morning for
     Northern Inland Waters Including The San Juan Islands.

     Small Craft Advisory from 1 PM this afternoon to 7 AM PST
     Thursday for Central U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 4 PM this afternoon to 7 AM PST
     Thursday for Puget Sound and Hood Canal.

&&

$$

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